Single-ply roofing systems have enjoyed great popularity due to their ease of installation, durability, and related advantages. Such roofing systems involve the installation of any of various elastomeric membranes such as EPDM, i.e., ethylene/propolyene/diene terpolymers, polyisobutylene, neoprene, and the like over roofing substrates which may include those formed from concrete, insulation board, sheet metal, and other materials.
In the past, such membranes have been installed by being covered with ballast, such as gravel, by the use of adhesives, and by having fasteners driven through the membrane into the underlying substrate. Such methods have obvious disadvantages. The use of ballast, for example, entails excessive roof loadings, while adhesive attachment involves a time-consuming, labor intensive, expensive operation. The use of fasteners destroys the seal of the roof, and leaks are difficult to control, notwithstanding attempts to provide waterproof sealing. Such problems have given rise to a number of attempts to provide roofing fasteners which do not compromise the weather integrity of roofing systems. Typical of such devices is that shown in U.S. Pat. No. 4,519,175 which includes an anchoring disc with a frusto-conical projection which is screwed or nailed on the roof's surface, following which an externally threaded, tined retainer cap is snapped thereover, fastening an interposed membrane to the disc. In a final step, an internally threaded cover is screwed over the retainer cap, locking the cap and thus the membrane to the roof. Such a system, however, has the drawback of involving a relatively large number of intricately shaped parts. Furthermore, as the parts multiply, so do the operations necessary for their installation, resulting in increased installation time and the expense connected therewith. Still another approach is that taught in U.S. Pat. No. 4,502,256, in which a two-part clamping system is taught involving a projecting stem member fastened to the roof over which a component whose operative member comprises a steel spring ring is snapped, fastening an interposed membrane to the roof. Although the latter system requires fewer components than does the former device, the nature of the spring ring connection and its counterpart stem component makes it susceptible to dislodgement, particularly in high wind conditions, when roof membranes are subjected to flutter. The exposed sharp ends of the spring ring also make accidental puncture of the membrane a distinct possibility.